Ship building at sand beaches started in the 1980's in Southern China. When building a ship at sand beaches, ship builders place wooden blocks on a sloped sand beach and start ship construction on top of these wooden blocks using land cranes. After the construction is complete, ship launching airbags, shown in FIGS. 1A and 1B, will be placed under the ship keel longitudinally between every two rows of the wood blocks. Inflating these airbags, the ship would be lifted off these wooden blocks. After the lifting operation, the wooden blocks will be then removed from under the ship keel. Once the holding lines are cut, the ship will be launched toward the sea along the slope with the rolling of these airbags. Before the launching, best efforts will be made to thoroughly search and remove metal debris from the site in order to protect the airbags. However, some steel debris with sharp edges will still escape the search and remain on the slope, and they can cut the rolling airbag and cause an explosion. In some cases, such explosion ended up in personal injury or even death.
The application of ship launching airbags has been broadened to other areas including ship repair in China and Southeast Asia. In an operation of pulling an old oceangoing ship onshore for repair and maintenance, a reverse operation of ship launching, some deflated airbags are placed at a sloped underwater floor and under the ship keel. There is a simultaneous combined operation of air injection and pulling of the ship onshore. During the pulling operation, airbags may be cut by the sharp edge of underwater metal debris on the sloped floor and/or the barnacles of oyster shells at the ship bottom, resulting in explosion accidents. Such accidents actually happen a lot, almost in every ship pulling operation.
Another newly-developed application of airbags is ship salvaging. During a ship salvaging operation airbags often face similar threats of cutting by various sharp edged objects inside the wrecked ship. For example, deflated airbags may be placed by divers at several designated locations inside the ship's cabin rooms. After connecting with a control system for air injection, airbags will produce a large amount of buoyancy and apply a high pressure force over a large area at one side of a cabin room. Sharp edged objects, such as the head of a cabin sprinkler at the ceiling, and/or damaged metals with sharp edges hanging at side walls, can cut and blow up the pressured airbags.
Similar to a pressured automobile tire, a pressured ship launching airbag may be damaged by these actions: cutting, puncturing and chopping. With automobile tires, the current designs have overcome the cutting and chopping issues by adding several layers of steel wires configured in cord plies embedded between two rubber sheets. Puncturing by a nail or other pointed sharp objects remains to be one un-resolvable issue for a tire. For ship launching airbags, however, the primary factor to cause its functional failure during various field applications is the cutting action by a sharp edge directly at the surface of a pressured airbag.
In most field applications, a cutting damage is the primary factor to cause the functional failure of a conventional ship launching airbag, usually leading to an explosion with considerable safety hazards. It becomes urgent and necessary to add an anti-cutting capability to ship launching airbags in order to eliminate potential safety hazards, while maintaining all its functionality in field applications.